Do we see accreting magnetars in X-ray pulsars?

TL;DR

This paper critically examines whether accreting magnetars with magnetic fields around 10^{14} G can be identified in X-ray pulsars, analyzing observational evidence and recent theoretical advances.

Contribution

It provides a critical review of claims for accreting magnetars and discusses how recent understanding of subsonic accretion challenges these claims.

Findings

Magnetic fields from observations are within 10^{12}-10^{13} G.

Evidence for accreting magnetars is not strongly supported by current data.

Recent models of subsonic accretion impact interpretations of magnetic field measurements.

Abstract

Strong magnetic field of accreting neutron stars ($10^{14}$ G) is hard to probe by X-ray spectroscopy but can be indirectly inferred from spin-up/spin-down measurement in X-ray pulsars. The existing observations of slowly rotating X-ray pulsars are discussed. It is shown that magnetic fields of neutron stars derived from these observations (or lower limits in some cases) fall within the standard $10^{12}$-$10^{13}$ G range. Claims about the evidence for accreting magnetars are critically discussed in the light of recent progress in understanding of accretion onto slowly rotating neutron stars in the subsonic regime.